A new series of maps of fog and low clouds covering the northern and central California coasts reveals daytime and nighttime patterns with a level of detail never previously mapped. U.S. Geological Survey scientists used new analyses of satellite images to understand the dynamics of fog.

Fog and low clouds have a significant influence on California’s coastal ecosystem processes and on the local economy for everything from wine production to tourism. The new digital maps can be used for a wide range of applications from siting solar panels to making decisions about what grapes to grow in coastal Calif. The patterns of fog and low clouds that are revealed by the new maps will help ecologists better understand coastal-to-inland plant and animal distribution. The fog and low cloud maps can delineate the commonly used term “fog belt” into zones with increased precision.

The maps were made using a decade's (1999 - 2009) worth of summertime satellite weather data. Over 26,000 hourly night and day images were classified to identify the presence of fog and low clouds and compiled for statistical analysis.

“We wanted maps that were as easy to use as the
USDA Plant Hardiness Zone Maps and as accurate as National Weather Service images so we compiled thousands of satellite images onto one map layer. People can pinpoint what fog zone their house or field is in. Montara (Calif.) is in the highest zone and gets, on average, more than 14 hours of fog and low clouds each day in the summer,” said Alicia Torregrosa, USGS geographer and lead author on the study.

The fog and low cloud data are freely available for download from the California Landscape Conservation Cooperative Climate Commons
website.